Non-destructive X-ray inspection machines for inspecting packaged products or, more simply, products, which hereinafter are intended, unless otherwise stated, as referring to the combination of the container and its content, are known.
For instance, the document US2006/0056583 A1 discloses a device for X-ray inspection of containers filled with products, for example beverages, in order to detect foreign bodies in such products, particularly at the bottom of the products.
According to this known document, the products to be inspected travel in line in a transport direction, handled by a handling system along a transport plane, and each product is inspected individually for detecting foreign bodies, which are characterized by having a different density with respect to the product density.
In particular, the known device has two X-ray beam emitters or sources arranged at predetermined positions above and below the transport plane, respectively, and arranged at an angle of 90 degrees of the beams emitted by both emitters when measured relative to the transport direction of the products.
The known device further comprises one or more sensors that are arranged beyond the goods to be inspected and are configured for receiving the X-rays after passing through the products.
The known device provides that the handling system consists of an X-ray transparent conveyor belt and two mutually facing, parallel straps configured for keeping the product by exerting a pressure against the lateral walls of the container, handling the products inside the device in which the inspection is carried out and transferring the products from the device to a conveying system outside the device.
The prior art presents some technical problems.
A first problem lies in the fact that the arrangement of the X-ray emitters above and below the transport plane does not guarantee the detection of foreign bodies, for example, at the upper part of the transported product.
The configuration proposed by the prior art document, which provides for angles between the emitters and the transport plane such that the center of the beams are tangent to the curvature of the bottom of the container, further has some drawbacks, as it is applicable solely to containers that are very high relative to their diameters. It is to be noted that, on the contrary, said configuration is not effective when the diameter of the products is large relative to their height, as at the proposed angle the metal cap of the container often overlaps the bottom in the obtained image, thus making it difficult to detect foreign bodies.
Another problem relates to the angle of 90 degrees of the beams emitted by both emitters relative to the transport direction of the products. Such angle, though simplifying the mechanical manufacturing of the system and the handling of the products, involves that the projection of a foreign body situated near the projection of a vertical wall of the container in one of the captured images is in the same position also in the other one and is consequently difficult to be detected because of the difficulty of separating, by means of numerical methods of image analysis, the projection of the foreign body from the projection of the vertical wall of the container, which is made for instance of glass or metal and is therefore radio-opaque.
A further problem relates generally to the use of straps for effecting transfer of the product onto and from the X-ray transparent inspection belt. Indeed, the supporting structure consisting of mutually facing straps is mechanically complex, differently transparent to X-rays and requires to be adjusted both in height and width in case it has to operate effectively on products with different diameter/height.
For instance, higher products need to be dragged by straps arranged at a higher position, whereas products with different diameters make it necessary that the surfaces of the straps are moved away from/brought close to one another.
A still further problem arises out of the fact that the straps, keeping the products by exerting a pressure against the lateral walls of the container, may damage or otherwise alter a label, if present, especially when this has been placed on the container in the step immediately prior to detection.
Solutions meant to handle/rotate the goods along the inspection belt for recording different images of each product taken from different perspectives are also known form other patent documents, for example from the patent U.S. Pat. No. 6,155,408.
According to such known solutions, it is provided that the walls of the container are acted upon for rotating or tilting it; as a consequence, also these known solutions suffer from the problems discussed above relating to the use of straps.
The Applicant has further observed that the rotation of the container does not guarantee simultaneous rotation of the product contained therein (and of the possibly present foreign body to be detected), especially when the content is a liquid.
From patent document EP 2256069 A1 a conveying apparatus is also known, which is to be used in non-destructive X-ray inspection machines for inspecting products and consists of a slat conveyor belt configured for providing a uniform print in the X-ray image.
This kind of conveying apparatus, even if it does not seem to solve one of the problems set forth above, has the problem of constituting a quite complex structure, more expensive in its manufacturing, generally having a more delicate structure and, in particular, being less versatile, as it is made especially for the indicated use.
In general, the Applicant has observed that the cited prior art is unable to effectively solve the problems set forth above.